A modern method of forming integrated circuit devices involves the formation of silicon devices in a thin film of single crystalline silicon material separated from a substrate of silicon material by a layer of buried oxide or insulator. This is commonly referred to as silicon on insulator construction or SOI construction. SOI construction allows for high performance silicon devices due to, among other reasons, the reduction in junction capacitance between diffused areas within the devices and the substrate.
The thickness of the buried oxide layer is an important consideration in SOI construction. If the buried oxide layer can be thinned, several advantages occur. Buried oxide layers are commonly formed by implanting oxygen through an outer surface of a substrate. The substrate is then annealed causing the implanted oxygen to react with the substrate to form the buried oxide layer. A thinner buried oxide layer can be formed using a lower dose of oxygen implant and thereby increase the throughput of the process used to form the buried oxide layer. A thin buried oxide layer also helps reduce the short channel effect involved with devices having channel lengths on the order of 5,000 angstroms or less. Devices having such short channel lengths commonly suffer from drain-induced barrier lowering due to field coupling through the buried oxide layer. By thinning the buried oxide layer, the short channel effect is reduced and the channel conductance is affected only by the gate electrode. An additional advantage of a thin buried oxide layer is that the thinner the buried oxide, the greater the heat dissipation through the substrate from the devices operating outwardly from the buried oxide layer.
The thinning of the buried oxide results in many advantages, but it is not without problems. First, the thinning of the buried oxide increases the drain to substrate capacitance which can result in reduced operating speeds of the devices formed outwardly from the buried oxide layer. Further, the thinner the buried oxide, the greater the risk of leakage through the buried oxide due to currents resulting from, for example, defects across the buried oxide layer.
Accordingly, a need has arisen for systems and methods for forming integrated circuit devices using SOI construction and thin buried oxide layers that prevent the disadvantages and problems associated with the thinning of the buried oxide layers.